I don't have that book anymore to look at the recipe but when I used to make tofu I had the best luck with the recipes and techniques from Asian Tofu by Andrea Nguyen. She goes into a lot of detail about every step. The earlier recipes I had used had the nigari added all at once, but she recommends adding 3/4 at first then stirring and pouring the last 1/4 directly into the areas that still look a bit milky. More can be added if that isn't enough. When I started doing it that way the curds became very distinct from the clear liquid and I had a higher yield whereas before I had a lot of cloudy liquid coming out while it was being pressed.
Asian Tofu is a big, beautiful hardcover — almost a coffee table book — but it has a lot of recipes with meat. The tofu-making chapter of AT is available as an ebook called Making Soy Milk and Tofu at Home. That may be a better bet. I just checked on Amazon and it's only $3.79!
If you have the Asian Tofu cookbook, you’ll recognize the contents of the eBook. It’s the extensive “Homemade Tofu Tutorial” chapter presented in both regular and enhanced (videos included) formats. I worked on that section of the book for months, perused a Ph.D. dissertation, and traveled to Asia to get a few questions answered too.